我创建了一个简单的程序,演示了我使用多重继承的Qt应用程序时遇到的运行时错误。继承树看起来像:
QGraphicsItem (abstract)
\
QGraphicsLineItem MyInterface (abstract)
\ /
\ /
MySubclass
以下是代码:
/* main.cpp */
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsLineItem>
//simple interface with one pure virtual method
class MyInterface
{
public:
virtual void myVirtualMethod() = 0;
};
//Multiple inheritance subclass, simply overrides the interface method
class MySubclass: public QGraphicsLineItem, public MyInterface
{
public:
virtual void myVirtualMethod() { }
};
int main(int argc, char** argv)
{
QApplication app(argc, argv); //init QApplication
QGraphicsScene *scene = new QGraphicsScene(); //create scene
scene->addItem(new MySubclass()); // add my subclass to the scene
Q_FOREACH(QGraphicsItem *item, scene->items()) // should only have one item
{
MyInterface *mInterface = (MyInterface*)item; // cast as MyInterface
mInterface->myVirtualMethod(); // <-- this causes the error
}
return 0;
}
调用我的接口方法时,Visual Studio中的调试会导致运行时错误:
Run-Time Check Failure #0 - The value of ESP was not properly
saved across a function call. This is usually a result of
calling a function declared with one calling convention with
a function pointer declared with a different calling convention.
知道问题是什么吗?
答案 0 :(得分:8)
因为您正在使用多重继承,所以指向vftable
的{{1}}指针实际上是指向MyInterface*
的指针。
QGraphicsLineItem vftable
可以解决问题,因为它会返回正确的dynamic_cast
vftable
一个简单的例子:
MyInterface* mInterface = dynamic_cast<MyInterface*>(item);
答案 1 :(得分:1)
如果您使用动态广告
,则会解决您的问题MyInterface* mInterface = dynamic_cast<MyInterface*>(item);
This questions处理各种C ++强制转换以及何时使用它们。在您的情况下,由于多重继承,您应该使用动态强制转换